Hatteras 38` FB/DC diesel tank inspection covers/manholes

[Lego]

Hello.

I have some questions regarding diesel holding tanks on our 38 FB/DC -74, situated in western Norway.
We have the two holding tanks aft, under the beds, and one "spare" tank in front of engineroom, between the engines.
This tank we dont need for diesel, and I am now planning to empty it, and use it for sewage holding tank, as we dont have this per now, and even in Norway this is mandatory.
As I started this work, I try to open the "manholes" on this sparetank. It is abt 20x20 cm brass plate, and well fitted with abt 20-25 bolts. I've managed to remove all except two bolts that i broke. Minor problem later.
Problem is I cant remove tha cover. Is it possible this is glassfibered to the tanktop?
Any ideas how to remove this manhole, any reply would be appreciated!
Issues regarding my plans will also be appreciated.

Thanks!

Lego

[MikeP]

If they are constructed the same way the tanks are on our 53, the top plates are glassed-in and cannot be removed except by cutting them out with a saw. The screws were used for initial assembly/layup but now do not serve any structural purpose.

[Bill Allen]

My 43 are the same way can't take the tops off. The plugs were hard enough getting off. Not sure why I'd even try to take the tops off. Bill

[Colwyn D]

Lego, the plate does not come off. If the tapped holes in the plate are not large enough for waste fittings then maybe drill them out and thread for your locally available sizes. I think my oem sizes are 1 1/2" npt for waste in and out, 1" for vent and a 3/4" plug drilled out for a contents/pressure gauge. The waste out uses a dip pipe that goes to the bottom of the tank and then a vacuum pump to discharge the waste underwater, this hose also has a tee fitted that goes to the deck level pump out fitting.
I did have a three way valve fitted to select either deck pump out or discharge underwater but found it a source of 'The Hatteras smell' so after renewing it twice just ditched it and fitted the tee.
As it happens I'm not that far from you at the moment, NW Hutton oilfield, North Sea. Not on the Hatteras though but a 14000t dive ship.

[Fanfare]

Ading a holding tank to a boat built before these tanks were required is difficult. My 1966 50MY needed one added. I have only two fuel tanks and most available space was already used for water or fuel. My Raritan LectraSan treatment units (added previously by me to comply with the Clean Water Act at a cost of over $5000) do a better job than many municipal sewage systems do, but government ignores this and forces compliance. As more and more US states declare no discharge zones I had to do something. I was able to buy a 25 gallon pre-made rectangular plastic holding tank which I could fit into a space in my gemerator room. It was more difficult finding a way to pump waste out of the tank. I had to move the refrigerator forward three inches and run the hose up to the deck. The hose runs are not what Jack Hargrave would have designed, but, other than a problem this spring, have worked. You will also need to plumb a vent line to the tank. Mine has a replacable Sealand odor filter on it, exiting through the engine room wall. I have not noticed any smells on deck. I have never changed the filter.

I have three heads. Two are on the LectraSans, the middle, the guest head, on the holding tank. In no-discharge zones everyone has to use the one toilet. We still use our original salt water flushes and the tank fills up pretty fast. Fresh water might use less water. A new Headhunter gauge with audible alarm has been a great addition. My plastic holding tank has been installed for 19 years and has not had a problem with odors.

We spend most of our time in the Bahamas, where I can send the guest head sewage over the side. We try to avoid using this toilet in favor of the LectraSans, which macerate, disinfect and bleach sewage with hypochlorous acid the unit makes by electrolyzing the salt in seawater.

For what it is worth, no-discharge zones are such an inconvenience for me that I try to take my business elsewhere. I am probably more interested in clean water than most--I swim in it. But the no-discharge zones are based on 1970s technology. Where would our cars be if government had dictated that there could be no innovation in exhaust emission technology? Unfortunately politicians seem to believe that sewage disappears down a black hole after it is flushed.

[Fanfare]

I have thought about your problem some more. If there is ANY place to fit a real holding tank I would recommend buying one. Hatteras fuel tanks were made with a different resin (fire resistent) than were the water tanks. It is probably OK to put water in a fuel tank, but not certain. Salt water is pretty corrosive and sewage is even worse. The pickup tubes in a diesel tank are probably too small for sewage and probably not made of the best material for this purpose and may leak and break off. The walls of the tank have had no thought given to sewer odor. You don't want your whole boat smelling like that. If your tank has a gauge it probably won't work well with "stuff" on it.

This question has come up on this forum before so I am sure someone has done it. I just think that if possible you are going to be better off and happier with a purpose-built holding tank.

[Lego]

First of all, thank you all for the replies!

And now the issues.
Yes, I've thougt of the fiberglass and odor issue, but I decided to give it a try, hence the space in our "big" 38' is getting smaller every season. I install new equipment nonstop, and the free space is getting smaller. To install a brand new plastic tank made for sewage purpose would be the best, but the work around would take to much effort to do.

The old FO tank is now cleaned inside, and is looking OK. The manholecovers is cleaned, and I managed to open all the plugs and pipe fittings. This gives me many opportunities regarding new piping and so on.I have two 2", two 1 1/4", and four 1" holes available.
The plan is to fit one 1 1/4" pipe thru one 2" reducer as suction, to the bottom of tank.
One gauge fitted in 1 1/4" hole, sewage purpose gauge this is, from Wema.
One vent line, 1", and filling from head connected either in the 2" or the last 1 1/4".
Suction from shore is postponed, due to lack of sewage stations in Norway. But easy installation later i guess.

To reduce risk of odor and leakage, I also plan to clean tank top properly, and apply one layer of polyester. This will eliminate the manhole cover bolt lekage that I caused when I tried to open the not openable! manhole.

I have also ordered a macerator pump, impellar type, and I hope this will do the job. The drawback will be suction height, but as long as I keep inside mounting instructions, I guess I'm good. I wonder if it is abolutely necessary to loop the overboard line over the sea water level? Overboard valve is under seawater level, in the keel.

Many wonderings and "what if's" still, but we build the road as we wander around.

Thanks again for the replies.
I took the liberty to rename the thread title.

Lego

[Colwyn D]

Glad you are moving ahead with your project. The macerator type pump will work, not sure of your voltage, but I had two of the cheaper 12v Jabsco type fail in two years, I then went to a diaphram suction pump, slower but much better and no problems getting a 'prime'. My outlet hose does not go above the water line but it would probably be wise if it did. You might consider a vent filter while you are installing the system. I made my own from solvent weld 3" pvc drain fittings filled with activated carbon available from pet shops. Have fun!

[Fanfare]

I have had a bilge pump back syphon and almost sink my boat so I have put raised loops and syphon breaks on all of these through hulls. The cause of the syphoning was heavily loading the boat for an extended trip which put the bilge pump hose under water. A passing wake probably pushed water up into the line starting the syphon. Luckily I was on board and heeded the bilge alarm. A holding tank would probably just fill itself up in this case and go no farther since the water can't get out. Still, you probably should have a vented raised loop here. These vents need checking and cleaning periodically, so put it somewhere you can easily reach it.

If Norway has few pumpout stations what do they expect you to do with your sewage? Dumb question--just like our government, that part is your problem.

[Lego]

Good idea about the activated carbon filter. Will probably put something like this together.
The macerator pump is of the cheap kind, with steel knives before the impeller. I think many people have had trouble with this type, specially if running dry for shorter or longer periods. Anyway, this is my first shot, and pump can easily be changed later.
Colwyn D: We work not far away from another. I am ERO on semisub. Bredford Dolphin. Bredford left Albert field last week, for yard stay. 5 year class renewal these days, and I am on my off-period , hurrying to get the boat ready for vacation.